Sony amp one channel crackling

[dayking79]

Hi all,

i bought an old Sony integrated amp last weekend from a flea market (was told it works perfectly). When i got it home one of the channels was crackling/popping, this noise started to get better with time as the amp started to get warm and then the noise had fanished after about an hour of play. Since that time, i have opened the amp up and gave it a good clean (sucked the dust, cleaned pots, and used contact cleaner on inputsetc).

I then turned the amp on for the second time and the crackles and pop's were quite a lot worse. Again they did get better with time but did not vanish this time. Ther was periods of time where there were no crackles/pop's but they came back throughout the listening session.

There are two big cap's that seemed to have a substance built up around where they meet the pcb, so i took them out and swapped them around to see if the noise would change channels but it did not.

Any ideas folks? BTW my electronic expertise is very very limited!

[rob3262]

Check ground connections/screws. Grounding issues often appear on Sony receivers.

[jgedde]

I had exactly the same problem with an old reel to reel unit I was repairing for a friend. I turned out, it was a transistor in the pre-amp section. I never did find out what the particular failure mode of the transistor was that caused this to happen...

If it goes away when the amp is hot, get a can of "freeze spray" and spritz it around. When the noise comes back, you're in the ball park.

rob3262 is right. Also, check the volume control pot. ..

[unclejed613]

check to see if the input diff pair is either 2SC945 (npn) or 2SA733 (pnp) transistors. sony used a lot of these, and many of the transistors of these two types had a habit of getting noisy like this. in particular, i've replaced a lot of 2SC945's over the years. in fact, at one time i kept a large quantity of 2SC1318 transistors in my parts bin as a replacement part. for whatever reasons, the C1318 didn't have the reliability problems that the C945 did. the complement to the 2SC1318 is 2SA720. these devices were the japanese equivalents of the "universal" transistors such as 2N2222/2905, 2N3904/3906, etc...

[duran_1960]

I faced same problem in my receiver-amp (Pioneer SX-750) .
These input transistors packed in one case with 5 pins. (2SA798) I think
their emiters unified so can I replace with two pnp equivalent ones?
and also can you advice to me european equivalents like begining with B.... something?
Thank you very much your kind helping in advance

[gmphadte]

Re-solder it

[duran_1960]

Ok.. Thank you I'll do it. But previously I cheked all transistors and capasitors and they are sems to be good! Soon or later I hope that find it.
Best regards

[Tony]

Originally posted by duran_1960
Ok.. Thank you I'll do it. But previously I cheked all transistors and capasitors and they are sems to be good! Soon or later I hope that find it.
Best regards

had the same problems with an old sansui, replacing to-92's cured the problem, btw, the replaced parts tested good on my multimeter...

[dayking79]

Thanks for all your comments guy's. Like i said, my electronic nous is low. The only component that i would say is the transistor is the ic chip that is connected to a big heat sink. It is a massive task to get to it, so before i try i need to know if this is the component you are talking about.
Thanks again.

[dayking79]

Ok, i think i have found what you are talking about. On the input board there are 3 pairs of transistors marked c1345. Could these be the problem?